In recent years, various computerized imaging systems have been proposed to convert an optical image of an object into a digital representation, such systems finding applications in medical imaging, in non-destructive testing, in aerial photography, etc. These computerized imaging systems are gradually replacing the conventional radiographic film exposure systems on the marketplace.
Such a system is disclosed in U.S. Pat. No. 5,150,394 to Karellas, which comprises a X-ray source delivering a beam of x-ray radiation toward a subject's body and a fluorescent screen receiving radiation passing through the patient's body and thus producing an optical image of the tissues and structures therein. This apparatus further comprises a single focusing element provided for focusing light emitted from the fluorescent screen toward a single array of optical sensors (CCD sensors), which generates a discrete electronic representation of the image produced by the fluorescent screen. Such a system has important drawbacks. With a single focusing element as proposed by Karellas, only one large array comprising a relatively high number of optical sensors can be used, thereby requiring to read each sensor of such a large array sequentially in order to generate a final electronic image. The sequential reading of the sensors implying a reading time proportional to the number of sensors to be read, such a single array system cannot provide fast processing as required in many imaging applications. Furthermore, in order to provide imaging of large Surfaces, although CCD arrays comprising many thousands of sensors are currently available on the marketplace, a larger area to be covered implies to separate further the focusing element from the object plane, thereby increasing overall dimensions of the image capture cartridge. The handling of such a cartridge and incorporation thereof into an x-ray exposing system could be rendered problematic due to large dimensions of such a cartridge.
In a second embodiment of his apparatus, Karellas teaches the use of a fiberoptic bundle for connecting adjacent areas of the image plane to the optical array. In order to increase the optical image surface covered by the apparatus while keeping the image resolution at an appropriate level, one can provide a plurality of fiberoptic bundles respectively connected to a plurality of optical sensors arrays, as disclosed in U.S. Pat. No. 5,159,455 to Cox. However, these fiberoptic bundles still cannot be integrated in a compact image capture cartridge. Moreover, the manufacturing of such a complex arrangement is critical, leading to increase the cost of such a system.
A different approach regarding the same problem is proposed by Yedid in U.S. Pat. No. 4,613,983, which consists of reconstructing a composite X-ray image from basic smaller images obtained by successive shots, using a source-receiver assembly displaceably movable along a predetermined path relative to a support for a body to be radiographed. Although such a system enlarges superficies of the optical image covered while keeping the resolution of the produced electronic image representation at an appropriate level, this system has the major drawback of requiring a plurality of successive exposure shots, leading to increase the time required to complete an image capture operation, and consequently increasing the risk that a movement of the patient's body during the capture operation causes a mismatch in the resulting composite image. Moreover, which such a system, the enlargement of the covered image superficies can be carried out only in the direction of displacement of the source-receiver assembly, thereby limiting the system capability to produce enhanced resolution images presenting regular dimensions.
Another conventional approach is discussed in U.S. Pat. No. 4,948,214 to Hamblen which consists of providing an array of focusing elements, each of these elements having a first end being optically coupled to a respective area of the optical image, and a second end optically connected to a respective one of a plurality of optical sensors arrays. However, in order to obtain appropriate image definition covering substantially all points of the optical image, while avoiding image overlapping, relatively large numbers of small diameter focusing elements are required, therefore requiring a large number of corresponding optical sensors arrays, leading to increase manufacturing costs. Moreover, this approach is generally limited to 1:1 magnification applications, thereby limiting the versatility afforded by this approach.
Another approach is disclosed in U.S. Pat. No. 4,349,248 to Rees, or in U.S. Pat. No. 4,512,632 to Tokomitsu, which consists of scanning an essentially linear array of focusing element relative to an object while transmitting the image thereof toward a corresponding linear array of optical sensors, and then reconstructing a complete electronic representation of the exposed object. While reducing the required number of focusing elements and associated optical sensors arrays, this approach is also generally limited to 1:1 magnification applications, and is characterized by a relatively slow image capture operation. Moreover, such a system incorporating electromechanical moving parts, it is relatively susceptible of mechanical failures.